1. Field of the Invention
The present invention relates to a congestion-responsive VoIP system and a congestion avoidance method for VoIP system. In particular, the present invention relates to a congestion-responsive VoIP system that can avoid congestion proactively by detecting congestion in early stages, and a congestion avoidance method for VoIP system.
2. Description of the Related Art
The ITU-T standard H225.0 defines the technology for determining a call coding method responsive to a congestion condition in an IP network. The technology for measuring service quality by use of RTCP reports is known. Examples of types of service quality that can be measured by use of RTCP include packet loss and jitter in arrival intervals. H225.0 proposes switching the medium coding method to the one that transmits at a lower speed or otherwise stopping a less important medium if a condition persists for a long period during which congestion spreads over a network due to an increase in packet loss or jitter in arrival intervals by use of RTCP.
In such a publicly known VoIP system as described above, congestion avoidance actions, for example, changing the coding method and stopping lower-priority channels, are conducted after the occurrence of delay in the arrival of packets and loss of packets. This means that the coding method changing action takes place reactively, instead of proactively, only after the degradation of speech quality has actually been caused.
Thus, the realization of a system is awaited that can avoid congestion proactively before congestion actually occurs by early detection of congestion. Such a system can desirably be implemented in a simplified way.